$vbulletin->session->vars['profileupdate'] not set correctly

[ub.ch]

Heya!

We did some changes to our profilefields a while ago and yesterday I was just checking how many of our users have already filled out the new fields.
To my suprise, there are a lot of user who have not yet filled them out, although they have been active since the changes.

I tried to refactor how the $vbulletin->session->vars['profileupdate'] var is set, but can't seem to find anything relevant.
All I could find was a line in functions.php which checks the fields and then, if the user has not filled them out, sets $vbulletin->session->set('profileupdate', 1);

But the function comment reads "Performs general clean-up after the system exits, such as running shutdown queries" [function exec_shut_down()]

So my question to you guys is, do you know where the profileupdate var is set? Is it possible to manually (?) set the var? When is exec_shut_down() called?

Thanks - as always - for your help!

Best
Malte